Ink jet printing is a non-impact method for producing images by the deposition of ink droplets in a pixel-by-pixel manner to an image-recording element in response to digital signals. There are various methods which may be utilized to control the deposition of ink droplets on the image-recording clement to yield the desired image. In one process, known as continuous ink jet, a continuous stream of droplets is charged and deflected in an imagewise manner onto the surface of the image-recording element, while unimaged droplets are caught and returned to an ink sump. In another process, known as drop-on-demand ink jet, individual ink droplets are projected as needed onto the image-recording element to form the desired image. Common methods of controlling the projection of ink droplets in drop-on-demand printing include piezoelectric transducers and thermal bubble formation. Ink jet printers have found broad applications across markets ranging from industrial labeling to short run printing to desktop document and pictorial imaging.
The inks used in the various ink jet printers can be classified as either dye-based or pigment-based. A dye is a colorant which is molecularly dispersed or solvated by a carrier medium. The carrier medium can be a liquid or a solid at room temperature. A commonly used carrier medium is water or a mixture of water and organic co-solvents. Each individual dye molecule is surrounded by molecules of the carrier medium. In dye-based inks, no particles are observable under the microscope. Although there have been many recent advances in the art of dye-based ink jet inks, such inks still suffer from deficiencies such as low optical densities on plain paper and poor light-fastness. When water is used as the carrier medium, such inks also generally suffer from poor water-fastness.
The ink jet receiving elements that can be used with the above mentioned inks must meet several requirements including producing high density images that will not smear, bleed or wander when exposed to water for short periods of time.
U.S. Pat. No. 5,560,996 relates to the use of a printing paper containing an intercalated compound that can chemically fix water soluble, cationic or anionic dyes to the paper by an electrostatic attraction between the dye and the intercalated compound. Although this type of an ink receiving layer does provide an image with good fixability, there is a problem with this material in that the overall density of the images generated is too low, as will be shown hereafter.
It is an object of this invention to provide an ink jet printing process for improving the fixability of an ink jet image so that it does not smear or wander when subjected to water for a period of time. It is another object of this invention to provide an ink jet printing process wherein the ink jet image is of high density.